The invention relates to dynamoelectric machines that incorporate amorphous metals in the core structure thereof, and more particularly relates to an amorphous metal stator structure including concentric cylinders formed of spirally or helically wound ribbon that is arranged to facilitate the mounting of one of the stator cylindrical components within the other. A method of manufacturing a dynamoelectric machine stator formed of concentric cylinders of amorphous metal is an aspect of the invention.
As the term amorphous metal is used herein it is meant to describe metals and metal alloys as well as metallic glass compositions that are formed by rapidly cooling from a molten state to a solid state so that there is no significant crystalline structure existing in the solidified state. In general, a cooling rate in the order of one million degrees Centigrade per second has been found suitable for manufacturing amorphous metal or metallic glass ribbon having a thickness of about 2 mils. More generally, depending upon the composition of a given amorphous metal, a suitable cooling rate may be in the range of 10.sup.5 C to 10.sup.8 C per second.
In the last several years a variety of methods have been developed for successfully forming amorphous metal ribbons of sufficient width and length to enable their use in making a variety of electromagnetic devices. In the early stages of development of such methods, the critical cooling rates needed to successfully form reasonably long strands of amorphous metal limited their application to the manufacture of very thin filaments. Examples of such prior art methods used to form filaments of amorphous metal are shown in U.S. Pat. Nos. 2,825,108 and 2,879,566 which issued, respectively, on Mar. 4, 1958 and Mar. 31, 1959. As explained in those patents, the methods disclosed involve feeding a thin stream of molten alloy onto either a chilled block or into a jetstream of chilled air in order to attain the necessarily rapid solidification of the alloy that prevents it from entering a crystalline state. Subsequently, other techniques were developed for applying continuous streams of molten amorphous metal to rapidly rotating chilled discs or cylinders to form substantially wider ribbons. At the present time, ribbons of amorphous metal up to two inches in width have been successfully formed in commercially useful lengths.
A summary of relatively recent technology relating to methods for making amorphous metal ribbons is presented in an article by Mr. J. J. Gilman, entitled "Metallic Glasses" which was published in the May 1975 issue of Physics Today, at pages 46 through 53. More recently, additional processes have been developed for manufacturing amorphous metal ribbons, having widths in the range of one-half to two inches, which are more adaptable for use in products that have relatively massive metallic body portions. Examples of some of those more recent processes and resulting ribbons are disclosed in U.S. Pat. Nos. 3,856,513, which issued on Dec. 24, 1974; 3,881,542, which issued on May 6, 1975; 4,059,441, which issued on Nov. 22, 1977 and 4,067,732 which issued on Jan. 10, 1978.
In addition to the evolution of manufacturing processes for making amorphous metal ribbons of widths that are useful in the manufacture of electromagnetic devices, it is explained in the above-noted article and in more recent publications such as an article by Mr. A. N. Martin entitled, "Metallic Glasses for the Electrical and Electronic Industries" which appeared in the January 1976, Vol. 37, issue of Engineer's Digest at pages 21 and 22, that considerable work has been done in developing amorphous metals having other desired characteristic properties such as improved ductility, thermal stability, and high magnetic induction. U.S. Pat. No. 4,036,638, which issued on July 19, 1977, discloses a number of binary amorphous alloys of iron or cobalt and boron that are characterized by having high mechanical hardness and soft magnetic properties while being free from embrittlement when heat treated in annealing processes. Annealing has been found to be a desirable way to stabilize the structure of amorphous metal ribbon used to form dynamoelectric machine stators. Another recently published article describing the current state of the art in amorphous metals useful in making products such as dynamoelectric machine stators is contained in Applied Physics, 49 (3), Part II, March 1978 at pages 1769 through 1774, authored by F. E. Luborsky, et al and entitled, "Potential of Amorphous Metals for Application in Magnetic Devices."
The properties of amorphous metal ribbons that make them particularly attractive for use in the manufacture of dynamoelectric machine stators is that such ribbons are mechanically strong and ductile and can be manufactured at relatively low cost compared with grain-oriented silicon steels of the types now commonly used to make such stators. It has been found that amorphous metal ribbon having suitably high magnetic induction can be formed of a composition such as Fe.sub.80 B.sub.20 which has one-fourth the magnetic losses of grain-oriented silicon steel, at a given induction for sinusoidally applied flux.
In addition to the information relating to amorphous metals given in the above-identified publications, several associates of the inventor named in this application have co-pending U.S. patent applications, which are also assigned to General Electric Company, and which disclose recent methods and compositions of materials for making amorphous metal ribbon that are particularly suited for use in the manufacture of dynamoelectric machine stators. Some of those patent applications also describe various stator and rotor structures formed of amorphous metal materials. For the convenient reference of the reader and to provide further background for the subject invention, several of those patent applications are identified below:
U.S. patent application Ser. No. 914,190, filed on June 12, 1978, (now abandoned) in the name of Thomas E. Lipo, entitled "Salient Pole Configuration for Use as a Reluctance Motor Employing Amorphous Metal" PA1 U.S. patent application Ser. No. 914,194, filed on June 12, 1978, (now abandoned in favor of continuation application Ser. No. 280,427, filed Nov. 19, 1980) in the names of Vernon B. Honsinger and Russell E. Tompkins, entitled "Slotless Motor Design Using Amorphous Metal" PA1 U.S. patent application Ser. No. 914,445, filed June 12, 1978, which issued on Aug. 25, 1981 as U.S. Pat. No. 4,286,188 in the names of Vernon B. Honsinger and Russell E. Tompkins, entitled "Amorphous Metal Hysteresis Motor" PA1 U.S. patent application Ser. No. 914,446, filed on June 12, 1978 (now abandoned) in the names of Vernon B. Honsinger and Russell E. Tompkins, entitled "Stator Design for Induction & Hysteresis Motors Using Amorphous Metal Tapes"
Although amorphous metal ribbons are commercially available having the desirable characteristics mentioned above, such ribbons also have inherent limitations that restrict their application in the manufacture of products such as dynamoelectric machine stators. One of the most significant limitations is that the relatively narrow widths of such available ribbons makes it necessary to form stator structures that incorporate a plurality of concentrically mounted edgewound ribbons in order to build enough metal into the structures to yield desired electrodynamic and thermal capabilities. In order to minimize the magnet reluctance and mechanical movement between such concentrically mounted cylinders, it is necessary to form a close tolerance fit between the abutting surfaces of the cylinders. Normally expensive precision machining operations are required to achieve such close tolerance fits; thus, it would be desirable to have available alternative means for achieving the same or better results at lower cost.
Another problem associated with the use of amorphous metal ribbon to form stator structures results from a need to provide winding receiving slots in the thin ductile ribbons so that an energizing winding can be mounted on the stator. Because of the thinness of these ribbons, which as noted above typically is in the range of one-half to two mils, it has been found that conventional stator lamination punching techniques are not readily suited to forming the winding receiving slots. Consequently, processes have been developed for forming slots in amorphous metal ribbons at the time they are cast; as explained, for example, in the U.S. patent application Ser. No. 903,140, which issued on May 22, 1979 as U.S. Pat. No. 4,155,397. When such slotted ribbons are edgewound in a helical form and stacked into cylinders to make a dynamoelectric machine stator, it is necessary to accurately align the slots to form axially-extending, winding-receiving slots while at the same time maintaining the outer diameter of the cylinder within a given tolerance so that it will cooperate in low magnetic reluctance relationship with a concentrically mounted cylindrical metal yoke. To achieve those objectives, it is usually necessary to either employ precision casting techniques that are expensive to perform, or to perform costly machining operations on the stator after the ribbon is wound into cylindrical form.
Accordingly, a primary object of the present invention is to provide a dynamoelectric machine stator formed of amorphous metal that overcomes the above-noted disadvantages of related prior art amorphous metal machines.
Another object of the invention is to provide a dynamoelectric machine stator having a plurality of different diameter, edgewound helical ribbons arranged to form, respectively, laminated cylinders of different diameters that are mounted concentrically within one another with a low magnetic reluctance junction between them.
Yet another object of the invention is to provide a dynamoelectric machine stator formed of an edgewound helical amorphous metal ribbon arranged in a cylinder with the individual turns thereof in frusto-conical shape, in combination with a second cylinder formed of amorphous metal ribbon disposed in low magnetic reluctance relationship around the exterior of the first cylinder.
Still another object of the invention is to rovide a dynamoelectric machine stator formed of helically wound, conically shaped coils of amorphous metal ribbon containing accurately aligned winding-receiving slots in the inner surface thereof.
A further object of the invention is to provide a method for manufacturing a dynamoelectric machine stator of a plurality of cylinders formed respectively of helically wound ribbons of amorphous metal, one of which is provided with conical turns to accurately adjust the diameter of its turns and to precisely align winding slots therein.
Additional objects and advantages of the invention will be apparent to those skilled in the art from the description of it that follows considered in conjunction with the accompanying drawings.